1. Field of The Invention
The present invention relates to a plunger pump having a plurality of plungers for discharging pressurized fluid by a reciprocating motion thereof. Specifically to a compact type of plunger pump in which low-pressure and high-pressure chambers for fluid are integrally formed in the casing thereof.
2. Description of The Prior Art
Recently, there have been proposed and developed various plunger pumps with a plurality of plungers to pressurize and discharge fluid such as oil by a reciprocating motion thereof. In such prior art plunger pumps, each of the plungers is reciprocated by a rotational movement of an eccentric cam whose cam surface abuts the mating surfaces of each plunger in such a manner that the above mentioned mating surfaces are normally biased to the above mentioned cam surface by means of a compression coil spring.
One such plunger pump is disclosed in the Japanese Patent First Publication (Tokkai) Showa 60-60370. The construction of such a plunger pump is shown in FIG. 1 illustrating its sectional view.
As schematically shown in FIG. 1, conventionally, the prior art plunger pump 1 is a two split type of plunger pump including a first half 1a wherein a low-pressure chamber 3 is defined, and a second half 1b wherein a high-pressure chamber 4 is defined. Referring now to FIG. 1, the low-pressure chamber 3 communicates through an oil passage 3b with an inlet port 3a which is connected through a conduit tube (not shown) to an oil tank (not shown), as is well known. A plurality of plungers 5 are provided in the first half 1a. Each of these plungers 5 is reciprocated by the rotational movement of an eccentric cam 6 whose cam surface abuts the mating surfaces of each plunger 5 such that the mating surfaces are normally biased to the cam surface by means of a compression coil spring 7a. The eccentric cam 6 is firmly fixed to a cam shaft 2 of the plunger pump 1. In general, the cam shaft 2 is driven by an engine (not shown) through a pulley (not shown) which is securely fixed by a woodruff key (not shown) inserted into a key-seat formed in the vicinity of the one end thereof. When the plunger 5 moves radially to the direction of the central axis of the cam shaft 2 in accordance with the rotational movement of the cam 6, openings 5a of the plunger 5 are exposed to the low-pressure chamber 3. Therefore, oil in the low-pressure chamber 3 is introduced into a pressurizing chamber 7. After this, as the plunger 5 moves away from the central axis, the openings 5a are closed and then the oil within the chamber 7 is pressurized. The pressurized oil is supplied from the chamber 7 via an oil passage 8 through a check valve 9 into a high-pressure chamber 4. The high-pressure oil in the chamber 4 is then supplied through an outlet port 4a into a driving element, for example, a control valve for controlling a steering gear of a power steering system.
In the above mentioned prior art plunger pump, as clearly seen in FIG. 1, the first half 1a for the low-pressure chamber 3 and the second half 1b for the high-pressure chamber 4 are separately formed. These halves 1a and 1b are connected to each other substantially at the center of the plunger pump assembly by a fastening means, such as bolts. However, in this construction, since both halves 1a and 1b are connected to each other by means of bolts, such a plunger pump assembly requires high-rigidity at the connecting portion because of the bolts. As a result, the plunger pump assembly must be of relatively large size. Such a plunger pump assembly tends to leak oil at the connecting section between the two halves 1a and 1b due to fluctuation in the tightening torque of the bolts. Furthermore, in the prior art plunger pump, there is the possibility that the fastening bolts may be loosened due to vibrations created during operation of the pump, thereby resulting in oil leakage. The prior art plunger pump requires a relatively long time for maintenance, because removal and installation of the fastening bolts is necessary.